NATURE OF STATISTICAL KNOWLEDGE 89 



time. If with a radical change in this one factor, 

 whilst all others remain, so far as may be, con- 

 stant, no change in the happening of the event is 

 observed, the experiment has shown that this 

 particular factor has no significant causal relation 

 to the happening of the event. If a marked 

 change in the happening of the event is observed 

 always to follow the change of conditions of 

 operation of the factor under investigation, then 

 clearly this factor plays a determinative part. 1 

 In other words, it is a fundamental logical pre- 

 requisite of the experimental method if it is to 

 be successful (that is, contribute to knowledge) 

 that it operate in a universe in which all causal 

 factors are not of equal quantitative significance 

 at any given instant of time. 



Clearly experimental analysis of this sort 

 would have quickly discovered, if the common 

 sense of men had not long previously shown, that 

 the course which a particular event is going to 

 take is not immediately the result of the action of 

 an indefinitely large number of individually in- 

 significant causal factors, but that it is the out- 

 come of the action of a few immediately deter- 

 minative factors and the effect of the indefinitely 

 large number of historically antecedent small 

 causes is insignificant in the sense of being differ- 

 ential. Generalized, the point may be put in 



1 Cf. Jennings' valuable paper on radical experimental analysis 

 already referred to in an earlier chapter (p. 13, supra). 



